Which of these arthropods are commonly associated with transmitting diseases?

Fleas are arthropods that play a significant role in the transmission of various diseases due to their parasitic nature and ability to bite. They are known to carry diseases such as the plague and typhus, as they can act as vectors, transmitting pathogens from one host to another. The flea's lifecycle and behavior make it particularly capable of spreading these diseases, as they can easily move from animals to humans and thrive in environments where they can feed on blood.

In contrast, caterpillars, beetles, and moths do not generally act as significant vectors for diseases in the same way that fleas do. Although some beetles can have harmful effects, they are not primarily known for transmitting diseases to humans or animals like fleas are. This distinction highlights the importance of recognizing the specific roles that various arthropods play in disease transmission. Fleas stand out as a critical vector because of their direct interaction with hosts and the historical context of disease outbreaks associated with them.